1. Field of the Invention
This invention relates to liquid polymeric compositions comprised of graft copolymers of starch and vinyl monomers. The compositions have high solids contents (25% by weight or greater) and are stable (show no excessive increase in viscosity and remain homogeneous) over extended periods of time. This invention also relates to processes for the production of the compositions and to processes using said compositions.
2. Initiators for Graft Polymerization
The production of graft copolymers of starch and vinyl monomers initiated by inducing free radicals on a starch is well known. Reviews have been published by J. C. Arthur, Jr. (Advances in Macromolecular Chemistry, Vol. 2, Academic Press, London & New York, pp. 1-87, 1970) and by G. F. Fanta (Block and Graft Copolymers, Vol. 1, John Wiley & Sons, London & New York, pp. 1-45, 1973).
A number of chemical activators are known. U.S. Pat. No. 3,138,564 to Borunsky discloses graft polymerization of 1,3 butadiene and acrylonitrile to starch using ozone and Fe(II). British Pat. No. 869,501 discloses the production of starch graft polymers utilizing polymerization initiators such as hydrogen peroxide, organic peroxides, hydroperoxides and dilute solutions of ceric ions. Yields may be improved by the use of an activator for these initiators such as mild reducing agents, e.g., ferrous ammonium sulfate, sodium formaldehyde sulphoxylate and the like. C. E. Brockway (Am. Chem. Soc. Div. Org. Coatings Plast. Chem., pp. 502-508, 1967) and U.S. Pat. No. 3,061,471 to Brockway et al. and 3,061,472 to Brockway disclose the use of hydrogen peroxide to graft polymerize various vinyl monomers onto starch. Additionally, C. E. Brockway, (J. Polymer Sci.: Part A, Vol. 2, pp. 3721-3731, 1964) discloses use of hydrogen peroxide to graft polymerize methyl methacrylate to starch. For the most part these initiators are nonspecific and induce homopolymerization of single monomers and copolymerization of monomer mixtures as well as the desired graft polymerization of monomer and monomer mixtures to the starch. This produces products which tend to separate on storage.
Such problems can be minimized or avoided by the use of a Cerium(IV) initiator. Although some homopolymerization has been reported using Cerium(IV) by Fanta, et al. (J. Appl. Polymer Sci., Vol. 10, pp. 919-937, 1966) the most important pathway for Cerium(IV) initiation of free radicals as outlined by Fanta (Block and Graft Copolymers, Vol. 1, p. 3, Ed. R. J. Ceresa, John Wiley & Sons, London & New York, 1973) would be expected to give graft copolymers to the exclusion of any homo- or copolymers. Extensive use has been made of this system to graft vinyl monomers to starch.